In diesel engines for automobiles, it is essential that the engine be stopped without delay in the event that the engine is accidentally reversed. When the diesel engine is reversed, an oil pump directly connected to the engine is also reversed so that the delivery pressure of the pump is lowered. It is possible to detect the reversing of the diesel engine through the detection of lowering of the delivery pressure of the pump, and by operating an actuator for stopping the engine in response to the detection of the lowering of the oil pressure by means of a pressure switch, the engine can be stopped without delay after the reversing. An example of such stopping device is shown in Japanese Patent Laid-open No. 1522/1973.
Another known automatic stopping device incorporates a vacuum pump connected to the diesel engine, adapted to produce a vacuum output by which braking mechanism is actuated. When the engine operates in the correct direction, a vacuum greater than a predetermined level is produced at the suction side of the vacuum pump. However, as the diesel engine is reversed, a positive pressure is produced at the suction side of the vacuum pump. It is, therefore, possible to automatically stop the diesel engine when the latter happens to be reversed, by using, in combination, a pressure responsive means associated with the suction side of the vacuum pump and an actuator for stopping the diesel engine when a predetermined positive pressure is reached at the suction side of the vacuum pump. This type of automatic stopping device is shown in Japanese Utility Model Publication No. 53-24600.
These conventional automatic stopping device can stop the diesel engine automatically and without fail when the diesel engine is accidentally reversed, but involve a problem of impractically large time lag of operation. More specifically, the first-mentioned type device requires 2 to 4 seconds before the oil pressure switch operates after the commencement of the reversing, and the second-mentioned type of the stopping device requires also 2 to 4 seconds until the predetermined level of the positive pressure is reached at the suction side of the vacuum pump after commencement of reversing of the latter.